Gary Neal scores 24 points and drains six three-pointers as San Antonio turns a close game into a laugher in the second half. The team that has won Game 3 in a Finals tied at 1-1 has gone on to win 11 of the past 12 NBA championships. (Mike Ehrmann/Getty Images)

Tim Duncan blocked a shot by Miami Heat point guard Mario Chalmers, hustled to the baseline to recover the ball and slapped it ahead before diving into the stands. Kawhi Leonard then chased down the loose ball, diving into the front row along the sideline to save it.

The result was two Danny Green free throws, but the sequence embodied the scrappy and relentless effort the San Antonio Spurs used during a demoralizing run to demolish the Heat, 113-77, at AT&T Center to take a 2-1 lead in the best-of-seven series.

“Just because [Duncan’s] a little older doesn’t mean he’s lost his competitiveness or his professional will to compete,” Spurs Coach Gregg Popovich said. “That’s not going to stop.”

The Spurs didn’t necessarily need to have brilliant performances from Duncan, Tony Parker and Manu Ginobili — the three holdovers from the past three championship teams — because they got more than enough support from the likes of Green, Gary Neal and Leonard, a trio making their NBA Finals debut.

Green led all scorers with 27 points, Neal had 24 and Leonard had 14 points and 12 rebounds while continuing to harass LeBron James into another subpar performance.

The Post Sports Live crew debates whether the San Antonio Spurs or the Miami Heat are the better overall team. (Post Sports Live)

The team that has won Game 3 with the series tied 1-1 has gone on to win the championship 11 of the past 12 times. The only team to lose in that scenario was the Heat, which lost the final three games against the Dallas Mavericks two years ago.

The Spurs haven’t lost consecutive games with Duncan, Parker and Ginobili in the lineup since mid-December. After an embarrassing 19-point loss in Miami two nights ago, San Antonio was able to keep that streak together despite getting a combined 25 points from its more accomplished trio.

“Huge win for us. It was just an all-around great team effort,” Duncan said. “We get our butts handed to us last game, and they played really well, and we came back here and change it up and just put together a great game all around.”

But Parker’s availability going forward is in doubt after the all-star point guard suffered a hamstring injury in the second half that forced him to leave the game momentarily. Parker revealed afterward he will have an MRI exam Wednesday.

“Hopefully it just got tight, and hopefully I will be fine,” Parker said.

The Spurs were able to withstand his absence because Miami’s all-star trio of James, Dwyane Wade and Chris Bosh never appeared to step off the plane from Miami.

“We got our butt whipped,” Wade said. “We got our butt kicked pretty good.”

James had four points at halftime for the second game in a row, with the long arms of Leonard and the pesky aggressiveness of Green forcing him to play out of rhythm. Other than an eight-point burst late in the third quarter, James appeared flustered and unable to find his desired spots to score. He settled for long jumpers and was tentative as he attacked the basket, which contributed to him finishing with just 15 points on 7-for-21 shooting.

“I think we’ve done a great job helping each other, team defense,” Green said of the Spurs’ scheme against James. “We know what kind of player LeBron is. We know he’s not at his best right now. But LeBron is not just us stopping him. He’s kind of stopped himself out there, and we’re getting a little lucky.”

The Spurs have tried to make James’s supporting cast beat them, but James has yet to find his groove through the first three games. James is averaging just 16.7 points in this series and has failed to score at least 20 points in three consecutive games for the first time since Games 3, 4 and 5 of the 2011 NBA Finals against Dallas, which humiliated him to the point that he responded with two more most valuable player awards, an NBA championship and an Olympic gold medal.

“I have to do better,” James said. “If I’m better, we’re better, and I have to be better. I’m putting everything on my chest and shoulders to be better. My teammates are doing a great job, and I’m not doing my part.”

Wade scored just four of his team-high 16 points in the second half, and Bosh had 12 points and 10 rebounds, but the Heat wasn’t able to get same contributions from its role players as it did in Game 2. Mike Miller was the only reserve to score in double figures; he made all five of his three-point attempts to finish with 15 points. Chalmers was held scoreless after providing 19 points in Game 2.

Without Miller, the game likely would have been over much earlier. He made three three-pointers in the first half, bringing the Heat within 43-42. Wade made a reverse layup to tie the game at 44, but the Spurs responded with back-to-back three-pointers to end the half, with Neal barely beating the shot clock to send his team into the locker room with a 50-44 lead.

The Heat bombarded the Spurs in Game 2 with an impressive 33-5 run in the second half, but the Spurs had a rebuttal of their own. They outscored Miami 33-10 over a 12-minute stretch from the second quarter and the third period, taking a 75-54 lead when reserve Cory Joseph stole a pass from James and made a layup. Popovich pulled his starters, but his team extended the lead to 37 when reserve DeJuan Blair made a two-handed dunk in the final minute.

“We got what we deserved,” Heat Coach Erik Spoelstra said repeatedly after the game. “Every shot they wanted to get, they got. . . . They played with more force and more focus. The teams that do that typically get what you deserve. They outplayed us, outclassed us from the very tip.”

Neal buried six of the Spurs’ NBA Finals-record 16 three-pointers. At the start of the fourth quarter, Neal hit a long three-pointer with Heat center Chris Andersen defending to put the Spurs ahead by 18, then came around a Matt Bonner screen to bury another three-pointer on the next possession to give the Spurs an 84-63 lead. At the time, Neal had matched Heat all-stars James and Wade in scoring.

Green, meanwhile, made seven three-pointers in Game 3 and is shooting 66.7 percent (16for 24) from long distance this series.